Camshaft For Detroit Diesel 71 Series Inline Engines: Controlling Valve Timing and Engine Operation

October 25, 2024

Camshaft For Detroit Diesel 71 (271, 371, 471, 671) Series Inline Engines: Controlling Valve Timing and Engine Operation

The camshaft is a critical component of the Detroit Diesel Series 71 engine, responsible for controlling the precise timing of the intake and exhaust valves. This timing is essential for ensuring efficient combustion and overall engine performance. The camshaft, through its lobes and gears, coordinates the opening and closing of the valves, allowing the engine to maintain proper air intake and exhaust expulsion during the two-stroke combustion cycle.

Camshaft Parts Catalog For 71 Series Inline Engines

Key Functions of the Camshaft:

Controlling Valve Timing:
- The camshaft controls the precise opening and closing of the engine’s intake and exhaust valves. The lobes on the camshaft push against the valve lifters, opening the valves at the correct time during the engine’s cycle. This allows fresh air to enter the cylinder and exhaust gases to exit the combustion chamber.
Coordinating Engine Timing:
- The camshaft is driven by the crankshaft through timing gears, ensuring that the valves open and close in perfect synchronization with the piston’s movement. This synchronization is essential to ensure efficient combustion and to prevent valve or piston damage from improper timing.
Driving Fuel Injectors (if applicable):
- In certain configurations, the camshaft also plays a role in driving the fuel injectors, ensuring that fuel is delivered to the combustion chamber at precisely the right moment. The camshaft lobes help time fuel injection events in line with the engine’s operation.

Below is a video of a camshaft being installed into a Detroit Diesel 671 Long Block

Components of the Camshaft:

Camshaft Lobes:
- The camshaft features lobes, or raised portions, which push against the valve lifters to open the intake and exhaust valves. The shape and height of these lobes determine the valve timing and how long the valves remain open.
Camshaft Bearings:
- The camshaft is supported by bearings located at various points along its length. These bearings allow the camshaft to rotate smoothly within the engine block, minimizing friction and wear.
Camshaft Timing Gear:
- The camshaft is connected to the crankshaft through a timing gear, which ensures that the rotation of the camshaft is synchronized with the crankshaft. This synchronization is essential for maintaining accurate valve timing.

Critical Tolerances and Measurements for the Camshaft:

Camshaft Lobe Height:
- The height of the camshaft lobes determines how far the intake and exhaust valves open. For the Detroit Diesel Series 71 engine, the camshaft lobes should be within 0.002 inches (0.05 mm) of the manufacturer’s specified height. Lobes that are worn or below this tolerance may result in poor valve operation, reduced power, and inefficient combustion.
- Measurement Process: Use a micrometer to measure the height of the camshaft lobes. Compare these measurements with the original specifications to determine if the lobes have worn beyond allowable limits.
Camshaft Journal Clearance:
- The clearance between the camshaft’s journals and the camshaft bearings must be maintained within strict tolerances to ensure smooth operation and minimize friction. The camshaft journal clearance for the Detroit Diesel Series 71 engine is generally between 0.0015 to 0.003 inches (0.038 to 0.076 mm).
- Measurement Process: Use a micrometer to measure the diameter of the camshaft journals and a bore gauge to measure the inside diameter of the camshaft bearings. Compare the difference to calculate the clearance. If the clearance exceeds the manufacturer’s specifications, the camshaft bearings may need to be replaced or the camshaft re-machined.
Camshaft End Play (Axial Clearance):
- The end play of the camshaft (the axial movement along its length) should be within a specific range to prevent excessive movement, which could disrupt timing and cause wear on the camshaft and its bearings. The acceptable end play for the camshaft is generally 0.002 to 0.010 inches (0.05 to 0.25 mm).
- Measurement Process: Use a dial indicator to measure the camshaft’s axial movement. If the end play is excessive, it may be necessary to replace thrust bearings or adjust the camshaft’s position within the engine.
Camshaft Runout:
- Runout refers to the amount of deviation from a true straight line as the camshaft rotates. Excessive runout can cause uneven wear on the lobes and bearings, resulting in poor valve timing and reduced engine performance. The camshaft runout should not exceed 0.001 to 0.002 inches (0.025 to 0.05 mm).
- Measurement Process: Mount the camshaft in a set of V-blocks and use a dial indicator to measure the runout at various points along the length of the camshaft. If the runout exceeds the allowable limits, the camshaft may need to be straightened or replaced.

Camshaft Inspection and Maintenance:

Visual Inspection for Wear and Damage:
- Inspect the camshaft for any signs of wear, scoring, or damage. Pay close attention to the camshaft lobes, journals, and bearings. Worn lobes can lead to improper valve operation, while scoring on the journals may indicate poor lubrication or the presence of debris in the oil.
- Look for any visible cracks or pitting on the camshaft lobes. Pitting may indicate improper heat treatment or material fatigue.
Measuring Camshaft Lobe Wear:
- Use a micrometer to measure the height of the camshaft lobes at multiple points along their length. If the lobes have worn beyond the manufacturer’s specifications, they may no longer provide the correct lift for the valves, leading to reduced engine performance. Replace or regrind the camshaft if necessary.
Checking Camshaft Bearings:
- Inspect the camshaft bearings for wear or scoring. If the bearings show signs of damage, they should be replaced to prevent excessive clearance and to ensure smooth camshaft rotation. Use a bore gauge to measure the inside diameter of the bearings and compare it to the camshaft journal diameter to ensure the proper clearance.
Inspecting the Camshaft Timing Gear:
- The camshaft timing gear is critical for maintaining synchronization between the camshaft and crankshaft. Inspect the teeth of the timing gear for signs of wear, chipping, or excessive backlash. If the gear teeth are worn, replace the gear to prevent timing issues.
Lubrication and Oil Passages:
- Ensure that the camshaft and its bearings are receiving proper lubrication. Check the oil passages within the engine block and camshaft for any blockages or sludge that could restrict oil flow. Proper lubrication is essential to prevent camshaft wear and to maintain smooth operation.

Camshaft Removal and Installation:

Removing the Camshaft:
- Before removing the camshaft, ensure that the engine’s timing has been marked to maintain proper alignment during reassembly. Drain the engine oil, remove the cylinder head, timing cover, and other components obstructing access to the camshaft.
- Removing the Camshaft Bearings: Once access to the camshaft is available, remove the camshaft bearings carefully. Take note of their position, as bearings must be reinstalled in the correct order. Use a puller tool, if necessary, to remove the camshaft.
Installing the Camshaft:
- Before installation, inspect the camshaft journals and lobes to ensure they are free from damage. Lubricate the camshaft and bearings before installation to prevent dry startup. Carefully insert the camshaft into the engine block, ensuring that the lobes and journals are aligned correctly.
- Timing Alignment: Ensure that the camshaft is properly aligned with the crankshaft using the timing marks. This alignment is critical for maintaining valve timing and preventing damage to the engine during operation.
Torqueing the Camshaft Bearings:
- Once the camshaft is installed, torque the camshaft bearings to the manufacturer’s specifications using a torque wrench. Ensure that the camshaft rotates freely within the bearings without excessive resistance or play.

Common Symptoms of Camshaft Problems:

Poor Engine Performance: Worn camshaft lobes can result in poor valve timing, leading to reduced engine power, misfires, or incomplete combustion. If the valves are not opening and closing correctly, the engine may experience a significant drop in performance.
Knocking or Tapping Noises: A damaged camshaft or excessive clearance between the camshaft and bearings can result in knocking or tapping noises during engine operation. This noise may indicate excessive wear or a failing camshaft.
Oil Pressure Issues: If the camshaft bearings are excessively worn or if the oil passages are blocked, the engine may experience low oil pressure, which can lead to improper lubrication of the camshaft and increased wear.
Timing Issues: If the camshaft timing gear is worn or if the camshaft is not properly aligned with the crankshaft, the engine’s timing may be off, resulting in misfires, poor power delivery, or even valve damage.

Conclusion On The Camshaft Section

The camshaft is essential for controlling valve timing and ensuring efficient combustion in the Detroit Diesel Series 71 engine. Regular inspection of the camshaft lobes, journals, and bearings is critical to maintaining proper engine operation. By keeping the camshaft within the specified tolerances for clearance, end play, and runout, engine operators can prevent major failures and ensure that the engine continues to run smoothly and efficiently for years to come.

Camshaft Parts Catalog For 71 Series Inline Engines

Please follow and like us:

We Deliver To Your Door In Canada

24 hr Worldwide Shipping

Success!

Camshaft For Detroit Diesel 71 Series Inline Engines: Controlling Valve Timing and Engine Operation